X-ray apparatus having means for supplying an alternating square wave voltage to the x-ray tube



Oct. 4, 1966 F. G. WEIGHART 3,277,302

X-RAY APPARATUS HAVING MEANS FOR SUPPLYING AN ALTERNATING SQUARE WAVEVOLTAGE TO THE X-RAY IUBI Original Filed May lO, 1965 2 Sheets-Sheet lTUBE HEAD F. G. WEIGHART Oct. 4, 1966 X-RAY APPARATUS HAVING MEANS FORSUPPLYING AN ALTERNATING SQUARE WAVE VOLTAGE TO THE X-RAY TUBE OriginalFiled May l0, 1963 2 Sheets-Sheet 2 llld mami,

BY www,

United States Patent O 3,277,302 X-RAY APPARATUS HAVING MEANS FOR SUP-lFLYING AN ALTERNATING SQUARE WAVE VOLTAGE TO THE X-RAY TUBE FrederickGordon Weighart, Brookfield, Conn., assignor to Automation Industries,Inc., El Segundo, Calif., a corporation of California Continuation of'application Ser. No. 279,362, May 10, 1963. This application Feb. 25,1965, Ser. No. 435,150 12 Claims. (Cl. Z50- 102) The present inventionrelates to an X-ray apparatus and, more particularly, to X-ray apparatuswhich is lightweight, compact, portable and permits accurate control ofthe wave length of its generated radiation.

This application is a continuation of co-pending application SerialNumber 279,362, X-Ray Apparatus, filed May 10, 1963, in the name ofFrederick G. Weighart and assigned of record to Automation Industries,Inc., now abandoned.

X-ray devices for inspecting industrial products and machine parts arecommonly used in the nondestructive testing industry. In recent years,the requirements for X-ray apparatus have become stricter. It has alsobecome desirable for the X-ray equipment to be of the socalled,portablevariety whereby it can be easily moved from one location to another.This has become very important for field testing purposes. However,portable X- ray equipment available heretofore has left much to bedesired.

As is well known, an X-ray tube requires the application of high voltagebetween the cathode and the anode in order to generate X-rays. Thisvoltage very frequently exceeds 100,000 volts. The components requiredto develop and handle voltages of such a magnitude mustmbe relativelylarge, well shielded andv well`insilat`ed.m For maximum portability, theX-ray apparatus should be capable of operating from a standardsixty-cycle power source. Step-up transformers capable of operating atsixty-cycles and developing voltages in excess of 100,000 volts are verylarge and heavy, and have greatlyreduced the portability of prior X-rayapparatus.

VThe penetrating power of X-rays is inversely proportional to their wavelength, and the wave lengths in turn are inversely proportional vto theanode voltage applied to the X-ray tube. Thus, when a sine wave isapplied between the anode and cathode of an X-ray tube, the wave lengthof the radiated emission will vary widely as the amplitude of the anodevoltage varies throughout the cycle. The hardest X-rays, i.e., thosehaving the shortest wavelengths, are produced at the peak of the sinewave and have the maximum penetrating power. During the portions of thecycles when the anode voltage is less than its'peak value, the X-raysare softer and have considerably less penetrating power. As a result inalternating X-ray systems available heretofore, there has been nocontrol over the spectral output of the X-ray tube and it has beenimpossible or extremely diflicult to achieve maximum penetrationefliciency.

It is one lof the primary objects of this invention to provide X-rayapparatus of improved portability.

It is a further object of this invention to provide an X-ray devicewhich can be operated from standard sixtycycle power sources but islightweight and easily transported from one location to another.

It is a further object of this invention to provide such a devicewherein the Wave length of the output radiation is controllable.

The manner in which the above Objects are achieved will be more apparentfrom the following description, the appended claims and the gures of theattached drawings, wherein: l

3,277,302 Patented Oct. 4, 1956 FIGURES 1 and 2 are schematic diagramsof an X- ray of a circuit apparatus embodying one form of thisinvention; and

FIGURE 3 illustrates the relationship between FIG- URES l and 2.

Before proceeding to a detailed description of the circuit of thisinvention, its general operation may be brieiiy described as follows:

The circuit is energized from a sixty-cycle power source which may beeither or 230 volts. This is applied to an input transformer whoseoutput controls the operation of the X-ray circuitry and also providessafety features and operator indications. The primary input to thetransformer is also applied to a D.C. power supply which, in theembodiment to be described, comprises a full wave rectifier. One side ofthe relatively low voltage D.C. source is applied to the center tap ofthe primary of the anode transformer. By means of the novel circuitry tobe described below, the ends of the transformer primary are alternatelygrounded to provide a square wave output from the secondary side at afrequency determined by the frequency of the alternate grounding.

The specific construction of the circuit of the invention will now bedescribed by reference to the drawing. Primary 60 cycle power input isapplied to the circuit at terminals 10 and is controlled by means of thedouble pole single throw switch 12 and the relay 14. The relay 14operates only upon the application of 230 volts A.C. to automaticallydouble the turns of the primary winding of auto-transformer 18.

Transformer 18 can receive either a 115 or a 230 volt input withoutswitching or internal wiring changes. The contacts 16 are illustrated intheir normal position with contact 16a closed. Upon the application of230 volts to relay coil 14, 16a opens and 16b closes, applying theinrlnut voltage to the entire primary winding of transformerEnergization of the transformer 18 also energizes a cooling blower 20and an indicating lamp 22 which provides a standby indication. Forfurther operation of the X-ray circuitry, a keyed switch 24 is providedfor purposes of safety. Closing of the switch 24 applies power directlyto one side of the actuating coil of relay 26.

An electrically operated timer motor 28 operates switches 30 and, whenthe timer is turned off zero, the contacts 301, 302 close. Switch 32then closes when transformer 34 is adjusted to minimum output. Thiscompletes the circuit to the coil of relay 26 so that contacts 271 and272 close.

Contact 271 serves as a holding contact to keep the relay 26 energizedwhen the kv. control transformer 34 is adjusted to operating voltage andswitch 32 opens. Contact 272 applies power to the primary of transformer36 and to kv. control transformer 34. When voltage is applied totransformer 34, it is also applied to the normally closed contact of aflasher 38 which intermittently operates the relay 40, causing thewarning lamp 42 to flash.

The output voltage from kv. control transformer 34 is applied to a fullwave rectifier circuit 44. The pulsating D.C. output is filtered by aninductor 46, smoothed by shunt-connected Icapacitor 47, and is appliedto the center tap 48 of the primary 50 of transformer 52 and to thecenter tap 54 of primary 56 of transformer 58.

The low voltage D.C. which is thus applied to the primaries oftransformers 52 and 58 is converted to A.C. by alternately grounding theopposite ends of each of the primary windings. This is accomplished bymeans of the trigger circuits to be described below. The frequency ofthe switching is the frequency of the induced alternating applied to theX-ray tube.

The trigger circuits used in this invention comprise a multivibrator, anemitter follower, a phase splitter and a converter. The multivibrator ofthis invention is of a standard design and includes a pair oftransistors 60. Its frequency is controlled within the range of 500 to650 cycles per second by means of a milliampere control 62 comprisingganged potentiometers 64, 66.

The supply voltage for the multivibrator is decoupled by inductor 68 andcapacitor 70. The collector voltage is maintained at a preset value 'bymeans of a suitable Zener diode 72. The width of each half cycle of thesquare wave output of the multivibrator is controlled by the duty cycleadjustment -control potentiometer 74. This control establishes theconduction time of transistor 60 and thereby controls the pulse durationof each transistor.

The square wave output from the multivibrator is applied by means of theemitter follower 76 to a phase splitter transistor 78. The outputs fromthe phase splitter taken over coupling capacitors 80, 82 from thecollector and emitter circuit, respectively, comprise two trains (a) and(b) of square wave pulses which are 180 degrees out of phase. Pulses (a)and (b) are each p-revented from going negative by means of the clippingdiodes 84, 86.

The base-line of each train is adjusted by the A.C. voltage level fromrectifier S5 as smoother by capacitors 87, 89 and received overconductor 91. Pulse train (a) is applied to the gate of asilicon-controlled rectifier 88 and pulse train (b) is applied to thegate of silicon-controlled rectifier 90u As the pulse trains (a) and (b)are 180 degrees out of phase, the silicon-controlled rectifiers 88, 90are alternately caused to conduct. As the rectifers 88 and 90alternately conduct, they connect the opposite ends of the primary 50 oftransformer 52 and the opposite ends of primary 56 of transformer 58 toground, thereby providing an alternating input at the switchingfrequency.

A commutating capacitor 92 is connected across the primaries -50` and 56of the transformers 52, 58. The slight delay introduced by the chargingtime of capacitor 92 permits each of silicon-controlled rectifers 88, 90to return to the blocking state.

Too rapid charging of the capacitor 92 is prevented by choke 94 at theoutlet of the D.C. power supply. Choke 96 limits transient peaks duringswitching and diodes 98 prevent negative peaks and oscillation.

The operating voltages for the X-ray tube 100` are supplied through theanode transformer 52 and the cathode filament transformer 5S. The A.C.voltage which is induced in each transformer secondary is variable inamplitude by variation of the input voltage controlled by variableauto-transformer 34.

In one embodiment of the invention, the actual D C. voltage fromrectifier 44 is variable between 15 and 60 volts and results in inducedsecondary voltages variable between 17.5 and 70 kvp. making the totalvoltage applied between anode and cathode during the on period of thetube equal to 35-140 kvp. Furthermore, it will be recognized that thevoltage which is supplied between the anode and cathode of the X-raytube has a square wave form. Accordingly, the radiation emitted by thetube is of a fixed wave length and thus has a constant penetrating powerthroughout each portion of its on cycle.

The anode current of the X-ray tube 100* is dependent upon cathodeemission which, in turn, is dependent upon filament temperature. Thefilament temperature is controlled by the series circuit of inductance102 and capacitance 104 which form a resonant circuit responsive to thefrequency of the secondary voltage induced in a separate filamentwinding S7 of transformer 58.

In the described embodiment the LC circuit is resonant at 650 cycles andat that frequency permits maximum current flow and maximum filamenttemperature. However, as the frequency is decreased, the LC circuitoffers a higher impedance, thereby directly reducing the curl rent flowand indirectly reducing the anode current. The operation of thisfilament control is disclosed and claimed in co-pending patentapplication, Serial No. 263,043, for Voltage Control, filed March 5,1963, by James F. McNulty, and assigned to t-he same assignee as thepresent application, now abandoned.

A thermal cutout switch 106 is included in that portion of the apparatushousing the X-ray tube 104i` for turning off all voltages when thetemperature of this portion of the apparatus exceeds a preselectedamount. When the thermal cutout 106 opens, the relay 26 is deenergizcd,opening switches 271, 272 and returning the unit to its standbycondition.

It will be understood by those skilled in the art that a number ofimportant advantages are achieved by the apparatus of this invention.

First, the apparatus is energized from a standard 60 cycle power sourcebut utilizes internal high frequency, produced by solid state circuitry,to reduce component sizes.

Second, the output spectrum from the X-ray tube is controlled by shapingthe high voltage wave form applied to the tube. In the illustratedembodiment, this applied voltage is in the form of a square wave toproduce Imaximum penetrating power. However, other wave shapes can alsobe employed, for example-a sawtooth wave would provide a linearfrequency change in the output radiation.

Third, the high voltage control is achieved solely in the low voltagecircuits. A novel approach is employed utilizing a controllable lowvoltage A.C. which is rectified to D.C. The D.C. is then appliedalternately between the center tap and each end of the primary windingof the anode transformer.

In addition to the foregoing, many other advantages of the invention aswell as many modifications and variations not departing from its spiritand scope, will be apparent to those skilled in the art.

It may be seen that the frequency at which the multivibrator runs may beconsiderably higher than the standard 60 c.p.s. power supply. This, inturn, will greatly reduce the amount of material required for the coresof the transformers and the conductors forming the various windings.Since the multivibrator and related equipment are all Iof the solidstate variety they are of a very small an-d lightweight variety. As aconsequence, the yoverall weight and size of the X-ray apparatus isgreatly reduced so that a high performance X-ray apparatus can be builtin a sufficiently small size to be portable.

Accordingly, the foregoing disclosure and description thereof are forillustrative purposes only, and donot in any way limit the inventionwhich is defined -only by the claims which follow.

What is claimed is:

1. X-ray apparatus of the class idescribed including the combination ofinput means adapted to be interconnected with a source of power,

square Wave generator .means coupled to the input imeans fo-r producinga low voltage train of square waves,

a step-up transformer having a primary winding and a secondary winding,said windings having a turnsratio which will provide a high tensionvoltage in the secondary winding,

said primary Winding being coupled to said square Wave generator meanswhereby the low voltage train of square Waves circulates in said primarywinding and produces a high tension train of alternating square wave inthe secondary winding,

an X-ray tube having an anode and cathode, and

means coupling said secondary winding to the said tube for coupling thehigh tension train of square waves to the anode, said high tensionsquare waves being effective to maintain the anode at a substan- 5.tially constant voltage Iwhen the anode is radiating X-rays.

2. X-ray apparatus of the class described including the combination ofinput means adapted to be interconnected with a source of power forreceiving -power therefrom7 pulse generator means interconnected withthe input means for producing a series of low voltage pulses of squarewave shapes,

a step-up transformer having a primary winding and a secondary winding,said windings having a turnsratio which will provide a high tensionvoltage in the se-condary winding, v

said primary winding being coupled to said pulse generator means wherebythe series of low voltage pulses circulate through the primary andproduce a train of high tension pulses in the secondary winding havingalternating polarities,

an X-ray tu-be having an anode and cathode,

means coupling said secondary winding to the tube for coupling the trainof high tension pulses to the anode, and

means in said pulse generator means to vary time durations -of thepulses of opposite polarity applied to the anode.

3. X-ray apparatus of the class described for inspecting a particularportion of a test piece, said apparatus including the combination of ahigh tension po'wer supply for producing a high voltage,

pulse generating means in said power supply for producing alternatinghigh voltage pulses having alternately opposed polarities and squarewave shapes, and

an X-ray tube having a cathode and anode, said tube :being coupled tosaid high tension power supply to form a self-rectifying circuit, saidanode being effective to radiate X-rays in response to the high voltagepulses, the amplitude of sai-d voltage pulses producing X-rays having awave length which will penetrate the portion of said test piece beinginspected.

4. X-ray apparatus of the class described including the combination ofinput means adapted to be interconnected with a source .of power forreceiving power therefrom,

pulse generator means coupled to the input means for producing a lowvoltage train of pulses having predetermined wave shapes,

a step-up transformer having a primary winding and a secondary winding,said primary winding being coupled to said pulse generator whereby saidlow voltage pulses circulate in said primary iwinding,

said secondary winding being coupled to said primary winding and havinga step-up turns-ratio whereby the low voltage pulse train in the primaryproduces a high tension voltage pulse train of alternating polarity inthe secondary winding having wave forms corresponding to the pulses insaid low voltage train,

an X-ray tube having an anode and cathode, and

means coupling the anode and cathode to said secondary winding forcoupling the high tension voltage to the anode whereby said anode isenergized corresponding to the pulses in the high tension volt-age.

5. X-ray apparatus of the class described `including the combination ofconverter means adapte-d to the interconnected with a source ofalternating power having a first frequency, said converter means beingeffective to produce a square wave having a frequency that is greaterthan the frequency of said source,

a step-up transformer having a primary winding and a secondary winding,said windings having a turnsratio which rwill provide a high tensionvoltage in the second winding,

said primary winding being coupled to the converte-r means `forreceiving the higher frequency square wave and producing a higherfrequency, high tension alternating square wave lin the secondary,

an X-ray tube having an anode and cathode, and

means coupling said secondary winding to said tube for coupling the highfrequency, high tension square wave to the anode.

6. X-ray apparatus of the class described including the combination ofrectifying means adapted to be interconnected with an .alternating powersource, said rectifying means being effective to rectify said power andprovide a direct voltage between the opposite sides thereof,

a step-up transformer having a primary winding and a secondary winding,said pri-mary winding having the center thereof coupled to one side ofthe rectifying means,

converter means interconnected with said rectifying means and theopposite ends of the primary winding, said converter means beingeffective to alternately interconnect the opposite ends of the primarywinding with the opposite sides -of the rectifying means at a frequencythat is higher than the frequency of said source to thereby produce ahigher frequency, high tension voltage in the secondary winding,

an X-ray tube having a cathode for generating free electrons and ananode for radiating X-rays, and

said means coupling the secondary winding to the anode to apply thehigher frequency, high tension voltage t-o said anode to accelerate thefree electrons whereby the tube radiates X-rays.

7. X-ray apparatus of the class described including the combination ofpower supply means adapted to be interconnected with a power source,said power supply means being effective to provide direct power,

frequency converter means interconnected with said power supply means toconvert said direct power i-nto a high frequency alternating power,

a step-up transformer having a primary winding and a secondary windingcoupled to the primary winding, said primary winding Ibeinginterconnected with the frequency converter for receiving the highfrequency power,

an X-ray tube having an anode and cathode, and means directly connectingthe anode and cathode to the secondary winding to form a self-rectifyingcircuit that includes the anode and cathode.

8. X-ray apparatus including the combination of rectier means arrangedto be energized from an A.C. power source at a first frequency to formD.C. .power supply means,

transformer means having a primary winding with a center tap between itsends and a secondary winding coupled to the primary winding,

switching means having a rst solid state controlled rectier connectedbetween one end of said primary winding and ground, and having a secondsolid state controlled rectifier connected between the other end of saidprimary winding and ground to alternately pass the D.C. output of saidpower supply means through said primary winding in opposite directions'to produce an A.C. Ioutput at a second frequency in the secondarywinding,

triggering circuit means having multivibrator means arranged to producea square wave output, phase splitter means activated by said square waveoutput to produce first and second out-of-phase triggering signalstogether with means for applying the first 'triggering signal t-o thegate of said rst rectifier and the second triggering signal to the gateof said second rectifier to alternately activate the gates of said firstand second s-olid state controlled rectifiers at a frequencysubstantially higher than said first frequency but less than radiofrequency, and

X-ray tube means connected to receive said A.C. output across its anodecathode cir-cuit.

9. X-ray apparatus including the combination of rectifier means arrangedto be energized from an alternating power source at a first voltage andfirst frequency to produce a D.C. output signal,

.relay means having a first position and a second position to connectsaid rectifier means for energization from a supply voltage, said relaymeans being responsi-ve to the magnitude of said voltage to move to oneposition when the voltage is at a first level and a second position whenthe voltage is at a second level,

transformer means having a primary winding and a secondary winding, saidprimary winding including a tap positioned between its ends,

means for applying one side of said D.C. output to said tap and theother side to ground,

a rst solid state controlled rectifier connected between a first end ofsaid primary winding and ground,

a second .solid state controlled rectifier connected between a secondend of said primary winding and ground,

multivibrator means arranged to produce a square wave output at a secondfrequency,

phase splitter means a-ctivated by said square wave output to producefirst and second out-of-phase triggering signals,

means for applying the first triggering signal to the gate of said firstcontrolled rectifier,

means for applying the second triggering signal to the gate of saidsecond controlled rectifier, and

X-ray tube means 4connected to receive said X-ray output across itsanode cathode circuit.

10. X-ray apparatus of the class described including the combination ofinput means adapted to be coupled to a source of alternating powerhaving a standard frequency,

rectifying means coupled to the input means for receiving thealternating power of vstandard frequency, said rectifying means beingeffective to rectify said alternating power and provide direct powerhaving a unipolar voltage,

converter means interconnected with said rectifying means tointermittently invert the voltage of the direct power and form a bipolarlsecond alternating power, 1

timing means coupled to the converter means to trigger the converter ata frequency which is higher than the standard frequency of said sourcewhereby the second alternating power will have said higher frequency,

a primary winding in a step-up transformer coupled to the -convertermeans for receiving the high frequency power,

a secondary winding in .said transformer coupled to the primary windingto produce a high voltage having said high frequency,

an X-ray tube having an anode and cathode, and

a self-rectifying -circuit coupling the secondary winding to the anodeand cathode.

11. X-ray apparatus of the class described including the combination ofCIK frequency converter means adapted to be interconnected with a lowfrequency power source, said converter means being effective to providealternating power having a frequency which is higher than the lowfrequency of said source,

frequency control means coupled to the frequency converter means forvarying the frequency of the higher frequency power,

a step-up transformer having a primary winding and a pair of secondarywindings, said primary winding being coupled to the frequency converterfor receiving the higher frequency power and producing a high tensionvoltage in the first secondary winding,

an X-ray tube having a cathode for producing free electrons and an anodefor radiating X-rays,

coupling means coupling the seco-nd secondary winding to the cathode forenergizing said cathode to produce the free electrons,

coupling means coupling the anode to the first secondary windings toapply the high tension voltage to said anode and accelerate the freeelectrons to the .anode whereby the tube radiates X-rays,

at least one of said coupling means including a frequency responsiveimpedance to vary the voltage thereacross .as the high frequency varies.

12. X-ray apparatus of the class described including the combination offrequency converter means adapted to be interconnected with a powersource having a standard low frequency, said converter means beingeffective to provide alternating power having a frequency which ishigher than the standard frequency of said source,

control means coupled to the frequency converter means for varying thevoltage of the higher frequency power,

a step-up transformer having a primary winding and a secondary winding,said primary winding being 'coupled to the frequency converter for`receiving the high frequency power having a controlled voltage andproduc-ing a controlled high tension voltage in the secondary,

an X-ray tube having a cathode for producing free electrons and an anodefor radiating X-rays, and

means coupli-ng the secondary winding to the anode to apply thecontrolled high tension voltage to the anode to accelerate the freeelectr-ons to the anode whereby the tube radiates X-rays.

References Cited by the Examiner UNITED STATES PATENTS FOREIGN PATENTS7/1935 Austria.

RALPH G. NILSON, Primary Examiner.

A. L, BlRCH, Assistant Examiner.

8. X-RAY APPARATUS INCLUDING THE COMBINATION OF RECTIFIER MEANS ARRANGEDTO BE ENERGIZED FROM AN A.C. POWER SOURCE AT A FIRST FREQUENCY TO FORMD.C. POWER SUPPLY MEANS, TRANSFORMER MEANS HAVING A PRIMARY WINDING WITHA CENTER TAP BETWEEN ITS ENDS AND A SECONDARY WINDING COUPLED TO THEPRIMARY WINDING, SWITCHING MEANS HAVING A FIRST SOLID STATE CONTROLLEDRECTIFIER CONNECTED BETWEEN ONE END OF SAID PRIMARY WINDING AND GROUND,AND HAVING A SECOND SOLID STATE CONTOLLED RECTIFIER CONNECTED BETWEENTHE OTHER END OF SAID PRIMARY WINDING AND GROUND TO ALTERNATELY PRESSTHE D.C. OUTPUT OF SAID POWER SUPPLY MEANS THROUGH SAID PRIMARY WINDINGIN OPPOSITE DIRECTIONS TO PRODUCE AN A.C. OUTPUT AT A SECOND FREQUENCYIN THE SECONDARY WINDING, TRIGGERING CIRCUIT MEANS HAVING MULTIVIBRATORMEANS ARRANGED TO PRODUCE A SQUARE WAVE OUTPUT, PHASE SPLITTER MEANSACTIVATED BY SAID SQUARE WAVE OUTPUT TO PRODUCE FIRST AND SECONDOUT-TO-PHASE TRIGGERING